The present invention relates to the field of camshaft adjusters. In particular, the present invention relates to a method for determining a scanning ratio for a characteristic curve for the operation of an electromechanical valve of a camshaft adjuster, to a computer program product for a motor controller, and to a data carrier with a corresponding computer program product.
For controlling a gas exchange, in a four-stroke combustion engine, a camshaft or control shaft is driven at half the engine speed of the crankshaft. Using its cams, the camshaft opens the gas-exchange valves constructed separately for pushing out the combusted gases and drawing in the fresh gases against the pressure in the cylinder and against the forces of the valve springs. The valves are activated in that the cams activate the valves mechanically. For this purpose, the camshaft is mounted in the combustion engine such that the cams mounted on the camshaft contact cam followers, for example, cup tappets, rocker arms, or finger levers that are in active connection, in turn, with the valves.
The coupling of a camshaft with the crankshaft is produced by a timing chain, a control belt, or a gear pair. Through this essentially rigid coupling, a fixed phase relationship is set between the rotation of the camshaft and the rotation of the crankshaft.
However, it has been shown that it can be advantageous for the operation of a combustion engine, in particular, with respect to fuel consumption and increase in power, to adjust this fixed phase relationship between the camshaft and the crankshaft during the operation of the motor. Through hydraulic or electric camshaft adjustment systems it is possible to adjust the phase relationship between the camshaft and the crankshaft when necessary. A hydraulic camshaft adjustment system has a camshaft adjuster and a valve. The camshaft adjuster operates according to the principle of vane cells and is placed between the control drive and the camshaft to be adjusted. For the case when there is no oil pressure in the combustion engine, e.g., when the motor is starting up, the camshaft adjuster still has mechanical locking. The locking position is located at an angular position within the adjustment region of the camshaft adjuster. The valve can be provided in the form of a central valve and controls the exchange of oil between the camshaft adjuster and the oil circuit of the motor. It is arranged in the center of the rotor. The arrangement of a valve in the motor, e.g., in the cylinder head, is also possible.
As soon as oil circulates around the central valve, the locking mechanism that connects a stator and a rotor of the camshaft adjustment system detaches in an undesired way, by which the rotor that is connected to the crankshaft can rotate relative to the stator that is connected to the crankshaft by the control drive.
A valve for a device for changing the control time of a combustion engine is known from the publication DE 10 2004 038 252 A1. Variable valve time behavior control devices are also known from the publications US 2002/0124821 A1 and US 2003/0010303 A1.
Known valves can produce incorrect adjustments during operation. The incorrect adjustment can lead to an uncontrolled opening of the locking, so-called middle locking, by which, for example, undesired noises could be generated in the camshaft adjustment system. These noises negatively influence the driving comfort of the vehicle.